Place your butter in the freezer for a minimum of 2 hours but preferably overnight.
In a jug mix together your water and lemon juice and set aside.
In a large bowl mix together the flour and salt. Now I’m going to sound like a home economics book but you need everything to be cold to yield a great pastry so feel free to put the bowl of flour in the fridge to chill.
On the larger side of a grater, grate the frozen butter directly into the flour mix. Stir the butter into the flour in with a knife. Frozen butter is my secret ingredient, the colder the butter the flakier the pastry. (Remember, this is a shortcut Rough Puff pastry, so we aren’t folding and doing that whole process. I’m all for process but if you get a great result with less work then I’m all for that.)
Add in the liquid, holding a little back just in case you don’t need it all. Using your hand bring your pastry together gently. You want to add just enough water to bring the pastry together. Too much water will not yield you a flaky dough.
Bring the dough together to form a ball. Wrap in cling film and place in the fridge for a minimum of 1 hour. You can refrigerate it for up to 3 days or freeze to use at a later day.
Note: Once you put the pastry in the fridge and it relaxes it will get a little wetter so factor that in.
While your rough puff pastry is chilling prepare your filling: Heat a large skillet to medium-high heat. Add in 2 tablespoons of butter and a handful of mushrooms, being careful not to overcrowd the pan. Leave the mushrooms undisturbed for 3-4 minutes.
Next, add to the pan 1/4 of the minced garlic, thyme, salt and pepper. Mix throughout and allow the mushrooms to continue cooking until fully cooked and caramelized, about another 4 minutes. Repeat this process until all of the mushrooms have been sauteed. Set cooked mushrooms aside.
In a medium bowl combine the ricotta cheese, egg and creme fraiche. Lastly, fold in the cooked mushrooms. Set aside.
Preheat the oven to 400°F (200°C) then line a baking tray with parchment paper. On a lightly floured work surface roll the pastry out to a 12-inch circle then fill the center of galette with the mushroom and cheese mixture, leaving a 1 1/2 inch border around the edges of the circle.
Gently bring the outer edges of the pastry up over the filling. Carefully transfer the galette to the lined baking tray then brush the crust of the galette with egg wash.
Bake the galette for 35-40 minutes or until the crust is a beautiful golden brown. Allow to cool for 10 minutes before slicing before serving.
Cover and store in the fridge for up to 3 days.